Re: [V2 PATCH 1/5] ACPI / scan: Parse _CCA and setup device coherency

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Tuesday, May 05, 2015 10:12:05 AM Suravee Suthikulpanit wrote:
> This patch implements support for ACPI _CCA object, which is introduced in
> ACPIv5.1, can be used for specifying device DMA coherency attribute.
> 
> The parsing logic traverses device namespace to parse coherency
> information, and stores it in acpi_device_flags. Then uses it to call
> arch_setup_dma_ops() when creating each device enumerated in DSDT
> during ACPI scan.
> 
> This patch also introduces acpi_dma_is_coherent(), which provides
> an interface for device drivers to check the coherency information
> similarly to the of_dma_is_coherent().
> 
> Signed-off-by: Mark Salter <msalter@redhat.com>
> Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
> ---
> NOTE:
>  * Since there seem to be conflict opinions regarding how
>    architecture should handle _CCA=0. So, I am proposing the
>    CONFIG_ARCH_SUPPORT_CCA_ZERO, which can be specified by
>    for each architecture to define behavior of the ACPI
>    scanning code when _CCA=0. Let me know if this is acceptable.
> 
>  drivers/acpi/Kconfig         |  6 +++++
>  drivers/acpi/acpi_platform.c |  4 ++-
>  drivers/acpi/scan.c          | 62 ++++++++++++++++++++++++++++++++++++++++++++
>  include/acpi/acpi_bus.h      | 11 +++++++-
>  include/linux/acpi.h         |  5 ++++
>  5 files changed, 86 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index ab2cbb5..dd386e9 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -54,6 +54,12 @@ config ACPI_GENERIC_GSI
>  config ACPI_SYSTEM_POWER_STATES_SUPPORT
>  	bool
>  
> +config ACPI_MUST_HAVE_CCA

ACPI_CCA_REQUIRED maybe?

> +	bool
> +
> +config ACPI_SUPPORT_CCA_ZERO

I guess this means "we support devices that can DMA, but are not coherent".
right?

> +	bool
> +
>  config ACPI_SLEEP
>  	bool
>  	depends on SUSPEND || HIBERNATION
> diff --git a/drivers/acpi/acpi_platform.c b/drivers/acpi/acpi_platform.c
> index 4bf7559..a6feca4 100644
> --- a/drivers/acpi/acpi_platform.c
> +++ b/drivers/acpi/acpi_platform.c
> @@ -108,9 +108,11 @@ struct platform_device *acpi_create_platform_device(struct acpi_device *adev)
>  	if (IS_ERR(pdev))
>  		dev_err(&adev->dev, "platform device creation failed: %ld\n",
>  			PTR_ERR(pdev));
> -	else
> +	else {

Please add braces to both branches when making such changes (as per CodingStyle).

> +		acpi_setup_device_dma(adev, &pdev->dev);

Why do we need to do that here (for the second time)?

>  		dev_dbg(&adev->dev, "created platform device %s\n",
>  			dev_name(&pdev->dev));
> +	}
>  
>  	kfree(resources);
>  	return pdev;
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 849b699..ac33b29 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -11,6 +11,7 @@
>  #include <linux/kthread.h>
>  #include <linux/dmi.h>
>  #include <linux/nls.h>
> +#include <linux/dma-mapping.h>
>  
>  #include <asm/pgtable.h>
>  
> @@ -2137,6 +2138,66 @@ void acpi_free_pnp_ids(struct acpi_device_pnp *pnp)
>  	kfree(pnp->unique_id);
>  }
>  
> +void acpi_setup_device_dma(struct acpi_device *adev, struct device *dev)
> +{
> +	int coherent = acpi_dma_is_coherent(adev);
> +
> +	/**
> +	 * Currently, we only support DMA for devices that _CCA=1
> +	 * since this seems to be the case on most ACPI platforms.
> +	 *
> +	 * For the case when _CCA=0 (i.e. is_coherent=0 && cca_seen=1),
> +	 * we would rely on arch-specific cache maintenance for
> +	 * non-coherence DMA operations if architecture enables
> +	 * CONFIG_ACPI_SUPPORT_CCA_ZERO.
> +	 *
> +	 * For the case when _CCA is missing but platform requires it
> +	 * (i.e. is_coherent=0 && cca_seen=0), we do not call
> +	 * arch_setup_dma_ops() and fallback to arch-specific default
> +	 * handling.
> +	 */
> +	if (adev->flags.cca_seen) {
> +		if (!coherent && !IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO))
> +			return;
> +		arch_setup_dma_ops(dev, 0, 0, NULL, coherent);

Oh dear.

What about

	if (adev->flags.cca_seen && (coherent || IS_ENABLED(CONFIG_ACPI_SUPPORT_CCA_ZERO)))
		arch_setup_dma_ops(dev, 0, 0, NULL, coherent);

I wonder how this is going to affect x86/ia64 too?

> +	}
> +}
> +
> +static void acpi_init_coherency(struct acpi_device *adev)
> +{
> +	unsigned long long cca = 0;
> +	acpi_status status;
> +	struct acpi_device *parent = adev->parent;
> +
> +	if (parent && parent->flags.cca_seen) {
> +		/*
> +		 * From ACPI spec, OSPM will ignore _CCA if an ancestor
> +		 * already saw one.
> +		 */
> +		adev->flags.cca_seen = 1;
> +		cca = acpi_dma_is_coherent(parent);
> +	} else {
> +		status = acpi_evaluate_integer(adev->handle, "_CCA",
> +					       NULL, &cca);
> +		if (ACPI_SUCCESS(status)) {
> +			adev->flags.cca_seen = 1;
> +		} else if (!IS_ENABLED(CONFIG_ACPI_MUST_HAVE_CCA)) {
> +			/*
> +			 * If architecture does not specify that _CCA is
> +			 * required for DMA-able devices (e.g. x86),
> +			 * we default to _CCA=1.
> +			 */
> +			cca = 1;
> +		} else {
> +			dev_err(&adev->dev, FW_BUG
> +				"DMA is not setup due to missing _CCA.\n");
> +		}
> +	}
> +
> +	adev->flags.is_coherent = cca;
> +	acpi_setup_device_dma(adev, &adev->dev);
> +}
> +
>  void acpi_init_device_object(struct acpi_device *device, acpi_handle handle,
>  			     int type, unsigned long long sta)
>  {
> @@ -2155,6 +2216,7 @@ void acpi_init_device_object(struct acpi_device *device, acpi_handle handle,
>  	device->flags.visited = false;
>  	device_initialize(&device->dev);
>  	dev_set_uevent_suppress(&device->dev, true);
> +	acpi_init_coherency(device);
>  }
>  
>  void acpi_device_add_finalize(struct acpi_device *device)
> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> index 8de4fa9..b804183 100644
> --- a/include/acpi/acpi_bus.h
> +++ b/include/acpi/acpi_bus.h
> @@ -208,7 +208,9 @@ struct acpi_device_flags {
>  	u32 visited:1;
>  	u32 hotplug_notify:1;
>  	u32 is_dock_station:1;
> -	u32 reserved:23;
> +	u32 is_coherent:1;
> +	u32 cca_seen:1;
> +	u32 reserved:21;

That will conflict with a patch I've already queued up, but never mind.

>  };
>  
>  /* File System */
> @@ -380,6 +382,13 @@ struct acpi_device {
>  	void (*remove)(struct acpi_device *);
>  };
>  
> +static inline bool acpi_dma_is_coherent(struct acpi_device *adev)
> +{
> +	return adev && adev->flags.is_coherent;
> +}
> +
> +void acpi_setup_device_dma(struct acpi_device *adev, struct device *dev);
> +
>  static inline bool is_acpi_node(struct fwnode_handle *fwnode)
>  {
>  	return fwnode && fwnode->type == FWNODE_ACPI;
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index b10c4a6..d14e777 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -583,6 +583,11 @@ static inline int acpi_device_modalias(struct device *dev,
>  	return -ENODEV;
>  }
>  
> +static inline bool acpi_dma_is_coherent(struct acpi_device *adev)
> +{
> +	return false;
> +}
> +
>  #define ACPI_PTR(_ptr)	(NULL)
>  
>  #endif	/* !CONFIG_ACPI */
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.